After 1957 Chamberlin, Powell and Bon were commissioned to prepare a detailed scheme for what is now the entire Barbican estate. (Their previous commissions had been confined to the south Barbican area south of Beech Street). In 1959 Chamberlin, Powell and Bon produced their report. (It is in the form of a fairly lavish book, with sketches, plans and photographs, which can be found on the shelves of the Guildhall Library). We know that, before producing the report, the partners travelled extensively, sometimes with members of the Barbican Committee. They visited Italy to view new housing developments in Milan, theatres in Verona and the City of Venice. In 1958 they toured European architectural sites and visited Stockholm, which had extensive pedestrian walkways and podia, and which was seen as a possible model for the kind of city the architects had in mind. Italian architecture influenced them. Christof Bon had worked in Italy with Ernesto Rogers, a well-known modernist architect, before joining the practice.
The Court of Common Council approved the Barbican Scheme on 11th November 1959. Subsequently the architects changed their design of the exterior of the buildings from polished concrete or ceramic material, to rough concrete. The Barbican estate, as eventually built, employed concrete in a much more monumental way than was envisaged in the comparatively delicate designs in the 1959 Report. There were other changes before the final look was achieved. The design of the towers underwent changes after 1959.